This application is based on Japanese Patent Applications No. 11-104688, No. 2000-014192 and No. 2000-036027 filed in Japan, the contents of which are incorporated hereinto by reference.
1. Field of the Invention
This invention relates to an epoxy resin composition and an encapsulant especially suited for the encapsulation of electronic devices severely required to have reliability, and an electronic device having an encapsulating member comprising a cured product of this composition.
2. Description of Related Art
In electronic devices such as semiconductor devices, semiconductor device components such as ICs (integrated circuits) or LSIs (large-scale integrated circuits) are encapsulated with resin. Epoxy resin compositions are chiefly used for such encapsulation.
In recent years, in order to make electronic devices low-costing, small-sized, light-weighted and also make them of high-performance and high-function, device components are being made to be mounted in a higher density, be more finely wired, be more multi-layered and be more multi-pinned, and being made to occupy a larger area in one package. With such progress, what is prevailing is being shifted from conventional pin-insert type packages such as DIP (dual in-line package) formed by transfer molding making use of solid epoxy resin, toward surface-mount type packages such as PPGA (plastic pin grid array), BGA (ball grid array) and CPS (chip size package). In some uses, bare-chip packaging has also been put into practice.
In such surface-mount packaging, liquid epoxy resin compositions are in wide use as encapsulants. Liquid epoxy resin compositions of this type are acid anhydride type epoxy resin compositions usually prepared using as base resins a liquid epoxy resin and an acid anhydride type curing agent advantageous for providing a low viscosity, and by mixing therein a curing accelerator and an inorganic filler and further appropriately mixing various additives such as a coupling agent, a colorant and a leveling agent.
Such acid anhydride type epoxy resin compositions, however, tend to cause an abrupt decrease in their adhesion to organic substrates or inorganic substrates in moisture resistance tests such as PCT (pressure cooker test), and tend to cause Interfacial separation due to a thermal stress that is produced because of a difference in coefficient of thermal expansion between resin, semiconductor chips and an organic substrate. Hence, electronic devices encapsulated with conventional acid anhydride type epoxy resin compositions have a disadvantage that they may have poor moisture resistance reliability and thermal-shock resistance.
The present invention was made taking account of such circumstances. Accordingly, an object of the present invention is to provide an epoxy resin composition having superior moisture-resistant adhesion and low-stress properties, an encapsulant comprising this composition, and an electronic device having a high reliability (moisture resistance and thermal-shock resistance), encapsulated with this encapsulant.
The present inventors made extensive studies on various curing agents and low-stress endowers in order to obtain an epoxy resin composition having superior moisture-resistant adhesion and low-stress properties. As the result, they have discovered that, where a curing agent containing a liquid aromatic amine is used as the curing agent and solid rubber particles are used as the low-stress endower, an epoxy resin composition can be obtained which has been improved In moisture-resistant adhesion to various substrates to have a superior reliability and may cause less decrease in heat resistance and have a higher low-stress effect than those making use of a liquid flexibilizer as the low-stress endower. Thus, they have accomplished the present invention.
The present invention provides an encapsulating epoxy resin composition comprising an epoxy resin which is liquid at normal temperature, a curing agent containing an aromatic amine which is liquid at normal temperature, rubber particles, and an inorganic filler; an encapsulant comprising this composition; and an electronic device having an encapsulating member comprising a cured product of this encapsulant.
The rubber particles may preferably be comprised of an acrylic rubber, and may more preferably be those having a core/shell structure. In particular, preferred in the present invention are particles of an acrylic rubber having a core/shell structure (i.e., core/shell type acrylic rubber particles) having a core comprised of a polymer which is rubbery at normal temperature and has a glass transition temperature of from xe2x88x9280xc2x0 C. to 0xc2x0 C. and a shell comprised of a polymer which is glassy at normal temperature and has a glass transition temperature of from 50xc2x0 C. to 150xc2x0 C.
The aromatic amine may preferably comprise at least one of 3,3xe2x80x2-diethyl-4,4xe2x80x2-dlaminodiphenylmethane and diethyltoluenediamine. These may each be used alone or may be used in the form of a mixture.